CHAP. XII THE COLOURS OF BIRDS 243 



food, there is at present no reason to doubt that 

 under ordinary circumstances the lipochromes of birds 

 are self-produced and not derived. 



Let us first consider the distribution of colour in 

 birds. The bright colours are largely, though by 

 no means exclusively, confined to the exposed parts 

 of the feathers. They may, however, occur on the 

 beak, the feet, and legs, the bare patches on the 

 head and neck of many birds, and even the parts of 

 the body which are covered with feathers, and the 

 mouth cavity. The colours in general fall into 

 three sets : — Those due to lipochromes, those due to 

 the dark melanins, and those which are structural. 

 The lipochromes when present tend to be uniformly 

 diffused, and are probably always in solution in the 

 abundant fats. It is an old observation that the 

 intensity of the red colour in the flamingo depends 

 upon the amount of oil contained in the feathers. 

 Besides occurring in the feathers, bill, feet, etc., lipo- 

 chromes usually colour the deposits of fat in the 

 body and the yolk of the eggs. 



The dark melanin pigments are very widely dis- 

 tributed in birds as in all Vertebrates. They occur 

 in the form of minute amorphous granules in the 

 epidermis or the cuticular structures, and not in- 

 frequently give rise to brilliant structural colour or 

 to very elaborate patterns and markings ; in some 

 cases they are uniformly distributed and give rise to 

 plain gray, brown, black, and related tints. Struc- 

 tural colours in birds are abundant, and include, in 

 addition to all metallic colours, blue, green, some 

 yellows, white, and in part the glossy black colours. 

 Blue, whether it occurs on feathers as in the jay, or 



